Method of manufacturing cylindrical body, friction stir welding method, and friction stir welding device

ABSTRACT

A method of manufacturing a cylindrical body, comprising the step of forming the cylindrical body by bending a plate-like work having first projected finger to fourth projected finger at four corned parts and allowing the end faces thereof to abut on each other, wherein the main surface of the cylindrical body on the side where sags are present is formed in an outer peripheral wall surface and the rear surface thereof on the side where the burrs are present is formed in an inner peripheral wall surface, and a first projected part is formed of the first projected finger and the third projected finger and a second projected part is formed of the second projected finger and the fourth projected finger. After the cylindrical body is held by friction stir welding devices, the probe of a friction stir welding tool is buried from the direction of either of the first projected part and the second projected part, and scanned in the direction of the other of the second projected part and the first projected part. The probe is buried and scanned in the state of being displaced to an advancing side.

TECHNICAL FIELD

The present invention relates to a method of manufacturing a hollowcylindrical body such as a vehicular wheel rim or the like byfriction-stir-welding, wherein end faces thereof are held in abutmentagainst each other by curving a plate-like workpiece, a friction stirwelding method which can appropriately be performed to manufacture sucha hollow cylindrical body, and a friction stir welding apparatus forsupporting a hollow cylindrical body during manufacturing of the same.

BACKGROUND ART

Wheels for mounting automotive tires thereon are manufactured by joininga disk formed as a circular plate and a wheel rim formed as a hollowcylindrical body to each other, by welding or the like. Such a wheel isreferred to as a two-piece wheel.

According to a method of manufacturing a wheel rim, as disclosed inJapanese Laid-Open Patent Publication No. 9-206951 and JapaneseLaid-Open Patent Publication No. 10-129204, a plate having an elongaterectangular shape is curved and opposite ends thereof are brought intoabutment against each other, producing a hollow cylindrical body, andthe abutting opposite ends (abutting regions) are resistance-welded bymeans of a so-called resistance butt welding process. According toJapanese Laid-Open Patent Publication No. 62-107832, it is proposed toform a hollow cylindrical body in the same manner as described above,and to join the abutting regions by MIG welding or TIG welding.

When abutting regions are welded by the welding processes disclosed inJapanese Laid-Open Patent Publication No. 9-206951, Japanese Laid-OpenPatent Publication No. 10-129204, and Japanese Laid-Open PatentPublication No. 62-107832, metal in the vicinity of the weld tends torise in a swelling formation. Since swelling makes the welded wheel rimlow in product quality, the welded wheel rim needs to be finished togrind off such swelling. Accordingly, wheel rims cannot be manufacturedefficiently using the disclosed welding processes.

Friction stir welding may be used to weld abutting regions, withoutproducing swelling on the welded assembly, and hence without the needfor finishing the welded assembly. According to a friction stir weldingprocess, a friction stir welding tool is rotated, and a probe on the tipend of the friction stir welding tool is plunged into abutting regionsof the end faces that are to be welded. Frictional heat is generated inthe vicinity of the abutting regions, causing a plastic flow of thematerial at the workpiece ends including the end faces thereof, so as tojoin the end faces to each other.

Because the probe is pressed into the abutting regions to be weldedduring the friction stir welding process, the abutting regions areliable to become spaced apart, tending to develop a clearancetherebetween. When such a clearance is formed, the welded strength islowered, thereby producing a welding defect.

In order to avoid the above shortcomings of the friction stir weldingprocess, a process for friction-stir-welding sheets, to press the endfaces of the sheets along a direction in which the rotating tool isdisplaced has been proposed, thereby preventing the sheets from becomingspaced apart, as disclosed in Japanese Laid-Open Patent Publication No.10-193139. However, although the proposed process is effective forjoining sheets together, it is not applicable to manufacturing a hollowcylindrical body, such as a wheel rim or the like.

According to the friction stir welding process, if the probe is plungedsuch that its central axis is aligned with the joint between abuttingend faces, then unjoined regions may remain in a probe operation surfaceand an opposite surface (reverse side) in the abutting regions. Whensuch unjoined regions remain, they reduce the bonding strength of theweld. If the bonding strength is excessively small, then the weldedassembly may possibly start to crack away from the weld when plasticmachining is performed on the workpiece. Japanese Patent No. 2808943proposes a process for avoiding welding defects produced by laserwelding using a filler. However, the proposed process cannot be used toavoid welding defects produced during a friction stir welding process,since a filler is not employed in the friction stir welding process.

According to one solution to the problem of remaining unjoined regions,it is customary to keep the tip end of the probe spaced from the reverseside of the workpiece, by a distance (gap) of 0.1 mm or less. However,providing such a small gap is not easy, and it takes a long time to formthe gap between the tip end of the probe and the reverse side of theworkpieces.

When a plate-like workpiece is curved and its opposite ends are broughtinto abutment against each other, producing a hollow cylindrical body tomanufacture a wheel rim, one of the opposite ends possibly may overlapwith the other end. A hollow cylindrical body with overlapping endscannot be joined by friction stir welding.

The above drawback can be eliminated by spacing the end faces slightlyapart from each other and then bringing them back into abutment witheach other, without causing overlapping, after the diameter of thehollow cylindrical body is slightly increased. However, carrying outsuch a process is tedious and time-consuming, and tends to lowerproduction efficiency of the friction stir welding process.

Another problem, even if opposite ends of the hollow cylindrical bodyare prevented from overlapping with each other, is that the hollowcylindrical body may have an elliptical cross-sectional shape, ratherthan a true circular cross-sectional shape. In this case, since thehollow cylindrical body does not have a true circular cross-sectionalshape, the welded workpiece cannot produce a usable product, or statedotherwise, product yield is lowered.

If the hollow cylindrical body has an elliptical cross-sectional shapethat is elongate horizontally, then as shown in FIG. 23, end faces 1, 2abut against each other while being positionally displaced, so as to beoriented toward a center of the cross-sectional shape while being spreadaway from each other.

It is a general object of the present invention to provide a method ofeasily and simply manufacturing a hollow cylindrical body, which is ofexcellent quality and appearance, according to friction stir welding,thereby efficiently manufacturing a hollow cylindrical body.

A major object of the present invention is to provide a friction stirwelding method, which is capable of preventing unjoined regions fromremaining, and hence being cable of producing a joint having asufficient bonding strength.

Another object of the present invention is to provide a friction stirwelding apparatus, which may be used for friction-stir-welding abuttingend faces of a hollow cylindrical body.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings, in which preferredembodiments of the present invention are illustrated by way of example.

DISCLOSURE OF THE INVENTION

According to a first aspect of the present invention, there is provideda method of manufacturing a hollow cylindrical body, comprising thesteps of:

bringing end faces of a plate material, having fingers projecting fromcorners along a joining direction, into abutment against each other toform protrusions projecting along the joining direction with end facesof the fingers, and also to form a hollow cylindrical body;

gripping the protrusions and friction-stir-welding abutting regions ofthe end faces to join the end faces to each other, thereby forming ahollow cylindrical body having protrusions; and

removing the protrusions.

According to the first aspect, when the plate-material having fingers iscurved, the fingers are brought into abutment against each other to formprotrusions, and then the abutting regions are friction-stir-weldedwhile the protrusions are gripped in place.

Since the protrusions are gripped in place while the friction stirwelding process is in progress, the abutting end faces (abuttingregions) of the hollow cylindrical body are prevented from becomingspaced from each other, or stated otherwise, the hollow cylindrical bodyis prevented from becoming opened. Therefore, the friction stir weldingprocess is easily and reliably performed.

The friction stir welding process makes it possible to join the abuttingregions without forming swellings. Therefore, the welded hollowcylindrical body does not need to be finished for smoothing out suchswellings. Consequently, it is possible to efficiently manufacture ahollow cylindrical body having a good appearance.

The hollow cylindrical body (W2) with protrusions should preferably bepressed from a side of an outer circumferential wall surface thereof,when the abutting regions are friction-stir-welded. Thus, the hollowcylindrical body is more reliably prevented from becoming opened andreturning to a plate shape.

In any case, the abutting regions should preferably befriction-stir-welded while the hollow cylindrical body is inclined withrespect to the horizontal direction. Since the area of contact betweenthe hollow cylindrical body and a friction stir welding tool used forfriction-stir-welding the hollow cylindrical body is reduced, thefriction stir welding tool is subjected to less load.

A preferred example of a hollow cylindrical body thus manufactured maybe a wheel rim, which is joined to a wheel disk to produce a vehicularwheel.

According to a second aspect of the present invention, a friction stirwelding process is provided, for bringing a first end face and a secondend face of a metal workpiece into abutment against each other, andthereafter joining the first end face and the second end face to eachother using a rotating friction stir welding tool, wherein when a firstend having the first end face is present on a retreating side and asecond end having the second end face is present on an advancing side, aworkpiece plunging member having a substantially circular cross sectionwhich is disposed on the tip end of the friction stir welding tool isplunged with a central region thereof, being displaced from a boundaryline between the first end face and the second end face to the secondend within a range equal to or smaller than the radius of the workpieceplunging member.

Since the workpiece plunging member is displaced from the boundary linesbetween the end faces within a range equal to or smaller than the radiusof the workpiece plunging member and is plunged into the second end(advancing side), the amounts of material stirred in the first end andthe second end are substantially equal to each other. Therefore, anunjoined region is prevented from remaining in the joined end faces, anda joint having excellent bonding strength is obtained.

Since an unjoined region is prevented from remaining, the managed valueof a gap may be increased. Therefore, an operation for forming the gapis quite easy to perform, and the time required to perform the operationis greatly reduced.

Plunging a probe into a region spaced from the abutting regions isdisclosed in Japanese patent No 3081817, Japanese Laid-Open PatentPublication No. 10-137952, and Japanese Laid-Open Patent Publication No.2000-225476. According to these conventional arrangements, the probe iswidely spaced from the abutting regions. According to the second aspectof the present invention, however, the distance between the boundaryline (abutting regions) between the first end face and the second endface and the probe (workpiece plunging member) is equal to or smallerthan the radius of the probe. The-present invention differs from theconventional arrangements in this regard.

The workpiece plunging member should preferably be displaced from theboundary line to the second end by a distance equal to or smaller thanone-half of the radius of the workpiece plunging member because theworkpiece plunging member thus displaced is more reliably effective inpreventing an unjoined region from remaining.

According to the second aspect, the end faces of different members,rather than the end faces of the hollow cylindrical body, may be joinedto each other. Specifically, a workpiece having the first end face and aworkpiece having the second end face may be separate from each other.The workpiece having the first end face and the workpiece having thesecond end face may be made of a chief component comprising the samemetal. Specifically, Al alloys having Al as a main component anddifferent auxiliary components may be joined to each other, e.g., anAl—Mg—Si alloy may be selected for the workpiece having the first endface, and an Al—Zn—Mg alloy may be selected for the workpiece having thesecond end face. Of course, Al and Al alloys may be friction-stir-weldedto each other.

According to a third aspect of the present invention, there is provideda friction stir welding process for bringing a first end face and asecond end face of a metal workpiece having a curved surface intoabutment against each other to form abutting regions, and thenfriction-stir-welding the abutting regions to join the end faces to eachother, wherein:

the first end face and the second end face have burrs projecting in athickness direction of the metal workpiece, and sags projecting in adirection transverse to the thickness direction;

when the abutting regions are formed, the sags of the first end face andthe second end face are disposed in confronting relation to each otherand positioned on an outer circumferential wall surface of the curvedsurface, and the burrs are positioned on an inner circumferential wallsurface of the curved surface; and

when the abutting regions are friction-stir-welded, a plunging member ofa friction stir welding tool is plunged into the outer circumferentialwall surface on which the sags are disposed in confronting relation toeach other, and thereafter the friction stir welding tool is moved toscan the abutting regions.

The surface where the sags are present is longer than the reversesurface by the projecting sags. If the metal workpiece is curved, suchthat the surface where the sags are present is positioned as an outercircumferential wall surface whose circumferential length is larger thanthe inner circumferential wall surface, then since the circumferentiallength of the outer circumferential wall surface is compensated for, anygap formed between the end faces can be reduced.

The reduced gap results in an increase in the area of contact betweenthe end faces. Therefore, when the abutting regions arefriction-stir-welded, a large amount of material is stirred, producing asufficient amount of frictional heat. Since the friction stir weldingprocess progresses easily, a large number of cavities are prevented frombeing formed in the joint. The joint thus maintains a desired bondingstrength, i.e., a product having excellent bonding strength is obtained.

The invention according to the third aspect is applicable tofriction-stir-welding the end faces of one member as well as joining theend faces of different members. Stated otherwise, according to the thirdaspect, the end faces of one metal workpiece may befriction-stir-welded. Specifically, if one metal workpiece has a firstend face and a second end face, then the abutting regions are providedby curving the metal workpiece to bring the first end face and thesecond end face into abutment against each other. Thereafter, theabutting regions may be friction-stir-welded.

According to a fourth aspect of the present invention, there is provideda friction stir welding apparatus for bringing end faces of a platematerial, having fingers projecting from corners thereof along a joiningdirection, into abutment against each other to form a hollow cylindricalbody having protrusions, and joining abutting regions to produce ahollow cylindrical body, comprising:

a base;

a first columnar member and a second columnar member which arevertically mounted on the base;

a support member inserted into the hollow cylindrical body havingprotrusions and being mounted on and extending between the firstcolumnar member and the second columnar member when the abutting regionsare to be friction-stir-welded; and

a first gripping member and a second gripping member supported on thesupport member for gripping the protrusions, respectively, which areformed when the fingers are held in abutment against opposite ends ofthe abutting regions of the hollow cylindrical body having protrusionsand which extend along a joining direction.

With the above arrangement, the protrusions of the hollow cylindricalbody can be gripped in place. Therefore, while the abutting regions arefriction-stir-welded, the hollow cylindrical body is reliably preventedfrom being opened.

Preferably, the first columnar member has a rotational shaft, and thesupport member has an end coupled to a rotary board fixed to therotational shaft, the friction stir welding apparatus comprising arotating mechanism for rotating the rotary board. Since the rotary boardis rotated by the rotating mechanism, the support member is turned.Therefore, the hollow cylindrical body, whose protrusions are gripped bythe first gripping member and the second gripping member, can easily bemoved to a location where the abutting regions are to befriction-stir-welded.

At least one of the first gripping member and the second gripping membershould preferably be displaceable toward or away from the protrusions bya gripping member displacing mechanism. The hollow cylindrical body caneasily be gripped in place simply by displacing the first grippingmember or the second gripping member.

The friction stir welding apparatus should preferably have outercircumference pressing members, for pressing the hollow cylindrical bodyfrom the side of an outer circumferential wall surface thereof, theouter circumference pressing members having a gap for inserting arotating friction stir welding tool for joining the abutting regions ofthe hollow cylindrical body. When the outer circumference pressingmembers press the hollow cylindrical body from the side of the outercircumferential wall surface thereof, the hollow cylindrical body isprevented more reliably from being opened. Therefore, the abuttingregions can easily and reliably be friction-stir-welded.

The friction stir welding apparatus should preferably have an outercircumference pressing member displacing mechanism, for displacing theouter circumference pressing members toward or away from the hollowcylindrical body. Since the outer circumference pressing members areeasily displaced by the outer circumference pressing member displacingmechanism, it is unnecessary to perform a tedious and time-consumingprocess for installation and removal of the outer circumference pressingmembers.

The support member should preferably be mounted on and extend betweenthe first columnar member and the second columnar member obliquely to ahorizontal direction.

Since the support member is mounted on and extends between the firstcolumnar member and the second columnar member obliquely, the hollowcylindrical body, which is gripped by the first gripping member and thesecond gripping member that are disposed on the support member, is alsoinclined. The area of contact between the hollow cylindrical body and afriction stir welding tool for friction-stir-welding the hollowcylindrical body is made smaller than if the hollow cylindrical bodywere supported horizontally. Consequently, the friction stir weldingtool incurs less load than if the friction stir welding tool were movedhorizontally.

According to a fifth aspect of the present invention, there is provideda friction stir welding apparatus for bringing end faces of a platematerial, having fingers at corners thereof, into abutment against eachother to form a hollow cylindrical body, and friction-stir-welding theend faces to each other, comprising:

a base;

first support means and second support means which are mounted on thebase;

a support member supported by the first support means and the secondsupport means;

pressing means supported by the support member, and movable forward orbackward by a displacing means, for pressing the hollow cylindrical bodyfrom the side of an inner circumferential wall surface thereof;

a support core supported by the support member, for insertion into thehollow cylindrical body and for supporting the hollow cylindrical body;and

a first gripping member and a second gripping member disposed on thesupport core, for gripping respective protrusions, which are formed whenthe fingers are held in abutment against opposite ends of abuttingregions of the hollow cylindrical body, and which extend along a joiningdirection.

According to the fifth aspect, after the hollow cylindrical body is setin the friction stir welding apparatus, the inner circumferential wallsurface of the hollow cylindrical body is pressed by the pressing means.When the inner circumferential wall surface of the hollow cylindricalbody is thus pressed, the abutting end faces of the hollow cylindricalbody are slightly spaced from each other. Since the abutting end facesare spaced from each other, the end faces are released from a stackedstate. Therefore, it is not necessary to perform a tedious andtime-consuming process, and the end faces can be friction-stir-weldedefficiently.

The pressing means may comprise a cam, which is movable forward orbackward as the displacing means moves forward or backward, a pluralityof rods engaging the cam and extending perpendicularly to the directionin which the cam is movable forward or backward, and pressers mounted onrespective distal ends of the rods, for pressing an innercircumferential wall surface of the hollow cylindrical body.

The support core should preferably have a discharge port defined thereinfor discharging a compressed gas. If the end faces of the hollowcylindrical body, which are eliminated from a stacked state and closedagain, are spaced from each other, then the compressed gas passesupwardly through a gap between the spaced end faces. If the end facesare held in abutment against each other, with no gap therebetween, thecompressed gas is blocked by the abutting end faces and does not passupwardly. Therefore, the pressure of the compressed gas increases. Theincrease in the pressure is detected by a pressure sensor, for example,making it possible to easily confirm whether the end faces are spacedfrom each other or not.

According to a sixth aspect of the present invention, there is provideda friction stir welding apparatus for bringing end faces of a platematerial, having fingers at corners thereof, into abutment against eachother to form a hollow cylindrical body, and friction-stir-welding theend faces to each other, comprising:

a base;

first support means and second support means which are mounted on thebase;

a support core spaced from the base by the first support means and thesecond support means, for insertion into the hollow cylindrical body andfor supporting the hollow cylindrical body; and

a first gripping member and a second gripping member disposed on thesupport core for gripping respective protrusions, which are formed whenthe fingers are held in abutment against opposite ends of abuttingregions of the hollow cylindrical body and which extend along a joiningdirection;

wherein either one of the first support means and the second supportmeans is movable toward or away from the support core by a displacingmeans.

With this arrangement, the longitudinal direction of the support coreand the direction in which a friction stir welding tool is displaced maybe aligned with each other. Stated otherwise, the hollow cylindricalbody may be set along the direction in which the friction stir weldingtool is displaced. Consequently, after the hollow cylindrical body isset on the support core, it is not necessary to position the hollowcylindrical body in alignment with the direction in which the frictionstir welding tool is displaced. Therefore, the friction stir weldingprocess can be performed quickly, and the efficiency thereof isincreased.

The first support means or the second support means is preferably guidedby a guide member while the first support means or the second supportmeans is displaced. The first support means or the second support meanscan thus be reliably displaced to a given location.

The first support means or the second support means should preferablycomprise natural lock cylinders. Such natural lock cylinders may havepiston rods, which are elevated and support the support core after thenatural lock cylinders are inactivated. When the cylinders aredisplaced, the cylinders are prevented from abutting against a certainmember.

The natural lock cylinders refer to cylinders having a mechanism forlocking a plunger under high hydraulic pressure.

According to a seventh aspect of the present invention, there isprovided a friction stir welding apparatus for bringing end faces of aplate material, having fingers at corners thereof, into abutment againsteach other to form a hollow cylindrical body, and friction-stir-weldingthe end faces to each other, comprising:

a base;

first support means and second support means which are mounted on thebase;

a support core spaced from the base by the first support means and thesecond support means, for insertion into the hollow cylindrical body andfor supporting the hollow cylindrical body;

a first gripping member and a second gripping member disposed on thesupport core for gripping respective protrusions, which are formed whenthe fingers are held in abutment against opposite ends of abuttingregions of the hollow cylindrical body, and which extend along a joiningdirection;

two aligning boards held in abutment against an end face of the hollowcylindrical body, and disposed one on each side of abutting regions ofthe hollow cylindrical body; and

aligning means having a cylinder for pressing the hollow cylindricalbody from the side of an opposite end face thereof, to displace thehollow cylindrical body until the one face of the hollow cylindricalbody abuts against the aligning boards.

With this arrangement, the aligning means makes it possible to position,easily and reliably, end faces of the hollow cylindrical body in thejoining direction. Thus, positional displacement of end faces of thehollow cylindrical body in the joining direction can be eliminated,without the need for a tedious and time-consuming process. The end facescan therefore be friction-stir-welded efficiently.

Either one of the first gripping member and the second gripping membermay be displaced by the cylinder. Thus, the number of parts making upthe friction stir welding apparatus is reduced, and the friction stirwelding apparatus may be constructed at a reduced cost.

The first gripping member or the second gripping member shouldpreferably be displaced and fit over the protrusion of the hollowcylindrical body after the displacement of the hollow cylindrical bodyis finished. The protrusions can thus be gripped without positionaldisplacements. Therefore, it is possible to manufacture a hollowcylindrical body of better dimensional accuracy.

According to an eighth aspect of the present invention, there isprovided a friction stir welding apparatus for bringing end faces of aplate material having fingers at corners thereof, into abutment againsteach other to form a hollow cylindrical body, and friction-stir-weldingthe end faces to each other, comprising:

a base;

first support means and second support means which are mounted on thebase;

a support member supported by the first support means and the secondsupport means;

a support core disposed on the support member, for being inserted intothe hollow cylindrical body and supporting the hollow cylindrical body;

a first gripping member and a second gripping member disposed on thesupport core, for gripping protrusions, respectively, which are formedwhen the fingers are held in abutment against opposite ends of abuttingregions of the hollow cylindrical body and which extend along a joiningdirection;

first pressing means supported by the support member, for pressing aninner circumferential wall surface of the hollow cylindrical bodyvertically downwardly with a resilient biasing means; and

second pressing means supported by the support member and displaceableby displacing means for pressing an inner circumferential wall surfaceof the hollow cylindrical body horizontally.

According to the eighth aspect, the inner circumferential wall surfaceof the hollow cylindrical body is pressed individually verticallydownwardly and horizontally. Since the hollow cylindrical body isstretched vertically downwardly and horizontally, the hollow cylindricalbody is prevented from becoming elongate horizontally and vertically.The hollow cylindrical body thus becomes truly circular, and can bemanufactured with an increased yield.

Vertical positional displacements of the end faces are also eliminated.Stated otherwise, the end faces are held vertically in good abutmentagainst each other. Cavities are prevented from being formed in thejoint, resulting in an increase in the product quality.

The friction stir welding apparatus should preferably have a presserstop means for pressing the hollow cylindrical body from the side of anouter circumferential wall surface thereof to a stop. Since not only theprotrusions of the hollow cylindrical body are gripped, but also thehollow cylindrical body is pressed from the side of the outercircumferential wall surface, the hollow cylindrical body is preventedmore reliably from being opened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a plate-like workpiece for forming awheel rim, having fingers on respective corners thereof;

FIG. 2 is an enlarged fragmentary vertical cross-sectional view showingan end of the plate-like workpiece shown in FIG. 1 at an enlarged scale;

FIG. 3 is a perspective view of a hollow cylindrical body havingprotrusions, which is formed by curving the workpiece shown in FIG. 1and bringing the fingers into abutment against each other;

FIG. 4 is an enlarged fragmentary vertical cross-sectional view showing,at an enlarged scale, end faces abutting against each other, with sagsas shown in FIG. 2 being held in abutment against each other on an innercircumferential wall surface, and having burrs extending from an outercircumferential wall surface;

FIG. 5 is an enlarged fragmentary vertical cross-sectional view showing,at an enlarged scale, end faces abutting against each other, with sagsas shown in FIG. 2 being held in abutment against each other on an outercircumferential wall surface, and having burrs extending from an innercircumferential wall surface;

FIG. 6 is a perspective view of a friction stir welding apparatusaccording to a first embodiment;

FIG. 7 is a front elevational view of the friction stir weldingapparatus shown in FIG. 6;

FIG. 8 is a plan view showing the manner in which a first grippingmember and a second gripping member of the friction stir weldingapparatus shown in FIG. 6 grip the protrusions of the hollow cylindricalbody shown in FIG. 3;

FIG. 9 is a plan view showing the manner in which a support member isturned and extends from a first columnar member to a second columnarmember, with the hollow cylindrical body disposed between the firstcolumnar member to the second columnar member;

FIG. 10 is a side elevational view showing the manner in which thehollow cylindrical body is pressed from the side of the outercircumferential wall surface by a prismatic rod member;

FIG. 11 is a plan view illustrating definitions of an advancing side anda retreating side;

FIG. 12 is an enlarged fragmentary cross-sectional view showing themanner in which a probe is plunged into abutting regions, with thecentral axis thereof overlapping a boundary line formed by the abuttingend faces of the workpiece;

FIG. 13 is an enlarged fragmentary cross-sectional view showing themanner in which the probe is plunged into the abutting regions, with thecentral axis thereof being displaced from the boundary line formed bythe abutting end faces of the workpiece toward the advancing side;

FIG. 14 is a perspective view of a friction stir welding apparatusaccording to a second embodiment;

FIG. 15 is a cross-sectional view taken along line XV-XV of FIG. 14;

FIG. 16 is a front elevational view of the friction stir weldingapparatus shown in FIG. 14;

FIG. 17 is a plan view of a horizontal pressing cylinder, a cam, and asmall rod for pressing the inner circumferential wall of the hollowcylindrical body;

FIG. 19 is a plan view of the friction stir welding apparatus shown inFIG. 14;

FIG. 20 is a cross-sectional view taken along line XX-XX of FIG. 15;

FIG. 21 is an enlarged fragmentary perspective view showing the mannerin which the end faces of the protrusion of the hollow cylindrical bodyshown in FIG. 3 are positionally displaced from each other along thedirection in which the end faces are joined;

FIG. 22 is an enlarged fragmentary perspective view showing the mannerin which the end faces of the protrusion of the hollow cylindrical bodyshown in FIG. 3 overlap each other; and

FIG. 23 is an enlarged fragmentary perspective view showing the mannerin which the end faces of a hollow cylindrical body are positionallydisplaced from each other along the vertical direction.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of a method of manufacturing a hollow cylindricalbody according to the present invention will be described in detailbelow with reference to the accompanying drawings in connection withfriction stir welding processes and friction stir welding apparatus thatare used for carrying out the method. In the embodiments, a wheel rim ofaluminum is manufactured as a hollow cylindrical body by way of example.

An elongate workpiece of aluminum is cut by shearing into a plate-likeworkpiece W1 of substantially elongate rectangular shape, as shown inFIG. 1. In the description below, cut surfaces that are exposed by thecutting are referred to as end faces denoted by respective referencenumerals 1, 2. A surface of the plate-like workpiece W1 that is visuallyrecognized in FIG. 1 is referred to as a main surface, and a surfacethereof that is reverse to the main surface is referred to as a backsurface. These main and back surfaces are denoted by respectivereference numerals 3, 4. In FIG. 1, the arrow A represents a joiningdirection referred to later, and the arrows B, C represent alongitudinal direction and a thickness direction, respectively.

As shown in FIG. 2 at an enlarged scale, the end faces 1, 2 of theplate-like workpiece W1 have burrs 5 a, 5 b projecting along thethickness direction C of the plate-like workpiece W1 and sags 6 a, 6 bprojecting along the longitudinal direction B (perpendicular to thethickness direction C) and having tip ends gradually curved. The burrs 5a, 5 b and the sags 6 a, 6 b are formed when the plate-like workpiece W1is sheared by a cutting tool in the above cutting process.

The burrs 5 a, 5 b extend from the back surface 4 along thicknessdirection C, and the sags 6 a, 6 b are displaced from central areas ofthe end faces 1, 2 in the thickness direction toward the main surface 3.Therefore, the length of the main surface 3 in the longitudinaldirection is slightly greater than the length of the back surface 4because the sags 6 a, 6 b are present.

First through fourth fingers 7 a through 7 d which are oriented in thedirections indicated by the arrow A are disposed respectively at thefour corners of the plate-like workpiece W1 (see FIG. 1). Statedotherwise, the first through fourth fingers 7 a through 7 d projectalong the joining direction.

The plate-like workpiece W1 thus shaped is curved along the directionsindicated by the arrow B until finally the end faces of the plate-likeworkpiece W1 are brought into abutment against each other, as shown inFIG. 3, forming a hollow cylindrical body W2 having a first protrusion 8and a second protrusion 9 that extend in the directions indicated by thearrow A. The first protrusion 8 is formed when the first finger 7 a andthe third finger 7 c have their end faces abutting against each other,and the second protrusion 9 is formed when the second finger 7 b and thefourth finger 7 d have their end faces abutting against each other.

If the hollow cylindrical body W2 is formed with the main surface 3facing as an inner circumferential wall surface and the back surface 4exposed as an outer circumferential wall surface, then as shown in FIG.4 at an enlarged scale, the sags 6 a, 6 b protruding in the directionindicated by the arrow C abut against each other on the innercircumferential wall surface. On the outer circumferential wall surface,there is developed a gap because it is free of the sags 6 a, 6 b and thecircumferential length of the outer circumferential wall surface and thecircumferential length of the inner circumferential wall surface aredifferent from each other when the plate-like workpiece W1 is curved.The gap reaches about 0.2 mm at maximum, resulting in a correspondingreduction in the area of contact between the end faces 1, 2.

According to the present embodiment, the plate-like workpiece W1 iscurved into the hollow cylindrical body W2 with the back surface 4facing as the inner circumferential wall surface and the main surface 3facing as the outer circumferential wall surface. Specifically, the mainsurface 3 that is longer in the directions indicated by the arrow B bythe sags 6 a, 6 b is exposed as the outer circumferential wall surfacewhose circumferential length is larger than the inner circumferentialwall surface, holding the heads of the sags 6 a, 6 b in abutment againsteach other.

As shown in FIG. 5 at an enlarged scale, the crests of the sags 6 a, 6 bare held in abutment against each other on the outer circumferentialwall surface, thereby preventing a gap from being developed in theabutting regions on the outer circumferential wall surface of the hollowcylindrical body W2. Stated otherwise, the area of contact between theend faces 1, 2 becomes larger than if the back surface 4 is exposed asthe outer circumferential wall surface.

Structural details of a friction stir welding apparatus according to afirst embodiment will be described below.

FIG. 6 is a perspective view of the friction stir welding apparatusaccording to the first embodiment, and FIG. 7 is a front elevationalview of the friction stir welding apparatus according to the firstembodiment. As can be seen from FIGS. 6 and 7, the friction stir weldingapparatus 20 comprises a base 22, a first columnar member 24 and asecond columnar member 26, a support member 28, a first gripping member30 and a second gripping member 32, and two prismatic bar members (outercircumference pressing members) 34 a, 34 b having projections. In FIG.6, the support member 28 is shown as being turned and released from thesecond columnar member 26. In FIG. 7, the support member 28 is shown asextending from the first columnar member 24 to the second columnarmember 26.

As shown in FIG. 7, the first columnar member 24 that is verticallymounted on the base 22 has a bottom board 36, L-shaped columnar members38 a through 38 d, a top board 40, and a rotational shaft 42 surroundedby the bottom board 36, the L-shaped columnar members 38 a through 38 d,and the top board 40. A plurality of bearings 44 are interposed betweenthe rotational shaft 42 and the bottom board 36. The top board 40 has athrough hole defined therein, and the rotational shaft 42 has a distalend portion projecting through the through hole upwardly of the topboard 40. The L-shaped columnar members 38 a through 38 d have asubstantially L-shaped cross section (see FIG. 6).

A substantially disk-shaped rotary board 46 is coupled to the distal endof the rotational shaft 42 that projects upwardly of the top board 40and spaced a predetermined distance from the top board 40 (see FIGS. 6and 7). As described later, the support member 28 is turned as therotary board 46 rotates in synchronism with the rotational shaft 42.

A bent support board 48 is coupled to side surfaces of the L-shapedcolumnar members 38 a, 38 c and the top board 40 (see FIG. 6). Brackets50, 50 are fixed to the support board 48. A cylinder 52 is angularlymovably supported on the brackets 50, 50.

The cylinder 52 has a rod 54 with a bracket 56 secured to a distal endthereof. A bent joint arm 58 is coupled to the bracket 56. The bentjoint arm 58 is coupled to the rotary board 46. In FIG. 7, the supportmember 28 is stacked on a slanted pedestal 60 having an upper end faceinclined upwardly by an angle of about 3° toward the second columnarmember 26. The support member 28 and the slanted pedestal 60 are coupledto the rotary board 46 upwardly of the rotational shaft 42. Thus, theslanted pedestal 60 is interposed between the rotary board 46 and thesupport member 28, so that the support member 28 is obliquely coupled tothe rotational shaft 42.

The support member 28 has a central region in the width directionthereof that is perpendicular to the longitudinal direction thereof, andthe central region is curved to project from opposite ends of thesupport member 28 (see FIG. 6). The inner circumferential wall of thehollow cylindrical body W2 is placed along the curved central region.

A cylinder support board 62 is fixed to the end of the support member 28that is stacked on the slanted pedestal 60. A cylinder 64 is coupled tothe cylinder support board 62.

The cylinder 64 has a rod 66 extending through a through hole defined inthe cylinder support board 62, and a presser plate 68 is mounted on thedistal end of the rod 66.

The first gripping member 30 is fixedly coupled to the presser plate 68.When the rod 66 of the cylinder 64 moves forward or backward, the firstgripping member 30 also moves forward or backward on the support member28. The first gripping member 30 has a recess 70 defined therein whichis complementary in shape to the first protrusion 8.

The second gripping member 32 is coupled to the upper end face of thesupport member 28 at a position that is a predetermined distanced spacedfrom the first gripping member 30. Stated otherwise, the second grippingmember 32 is positioned and fixed to the support member 28. The secondgripping member 32 has a recess 72 defined therein which iscomplementary in shape to the second protrusion 9.

The first gripping member 30 and the second gripping member 32 haverespective lower ends curved complementarily to the curved upper endface of the support member 28. Therefore, the first gripping member 30and the second gripping member 32 are prevented from being displaced inthe transverse direction of the support member 28.

The second columnar member 26 is vertically mounted on the base 22 andspaced a predetermined distance from the first columnar member 24 (seeFIGS. 6 and 7), and is higher than the first columnar member 24. Thosecomponents of the second columnar member 26 which are identical to thoseof the first columnar member 24 are denoted by identical referencecharacters, and will not be described in detail below.

A pedestal 74 having a slanted portion is disposed on the top board 40of the second columnar member 26. A stopper 76 for stopping angularmovement of the support member 28 is fixed to an end face of the topboard 40.

A first shaft engaging member 78 having a bent distal end is fixedlycoupled to the L-shaped columnar member 38 d of the first columnarmember 24. As shown in FIGS. 7 and 8, a second shaft engaging member 80is also fixedly coupled to the L-shaped columnar member 38 c of thesecond columnar member 26. The second shaft engaging member 80 is shapedsimilarly to the first shaft engaging member 78.

As shown in FIG. 7, a mount 83 having a bracket 82 is installed on thebase 22. A cylinder 86 is supported on the bracket 82 by a shaft 84.

The cylinder 86 has a rod 88 with a bracket 89 mounted on the distal endthereof (see FIGS. 6 and 8). A first arm 92 and a second arm 94 arecoupled to the bracket 89 by a rod 90 (see FIG. 6). Specifically, thefirst arm 92, the rod 88, and the second arm 94 have respective throughholes defined in their ends, and the rod 90 extends through thesethrough holes.

The first arm 92 and the second arm 94 have other through holes definedtherein at positions slightly closer to the support member 28 thanlongitudinally central regions thereof. A joint rod 96 (see FIG. 8)extends through these through holes and through holes that are definedin the first shaft engaging member 78 and the second shaft engagingmember 80, thereby coupling the first arm 92 and the first shaftengaging member 78 to each other and also coupling the second arm 94 andthe second shaft engaging member 80. The first shaft engaging member 78is held against a side surface of the first arm 92, and the second shaftengaging member 80 is held against a side surface of the second arm 94.

The first arm 92 and the second arm 94 have respective distal endportions extending to positions above the first columnar member 24 andthe second columnar member 26, respectively. The prismatic bar members34 a, 34 b that are spaced a predetermined distance from each otherextend from the distal end portion of the first arm 92 to the distal endportion of the second arm 94. The prismatic bar members 34 a, 34 b haveteeth extending from their opposite ends, and these teeth are placed onthe first arm 92 and the second arm 94 and coupled to and supported onthe first arm 92 and the second arm 94.

As described later, the prismatic bar members 34 a, 34 b function asouter circumference pressing members for pressing the outercircumferential wall surface of the hollow cylindrical body W2 (seeFIGS. 2 and 3). A friction stir welding tool 100 for welding abuttingend faces of the hollow cylindrical body W2 is inserted in a gap 98 (seeFIGS. 6 and 8) between the prismatic bar members 34 a, 34 b.

The friction stir welding tool 100 has a rotor 102 (see FIG. 6) fixed toa spindle, not shown, and a probe 104 mounted on the tip end of therotor 102.

A friction stir welding process for joining the hollow cylindrical bodyW2 and a process of manufacturing a wheel rim are performed using thefriction stir welding apparatus 20 thus constructed, as follows:

First, the hollow cylindrical body W2 with the first protrusion 8 andthe second protrusion 9 formed thereon is placed onto the support member28 with the first protrusion 8 being positioned ahead. Thereafter, thesecond protrusion 9 is fitted into the recess 72 in the second grippingmember 32.

Then, the cylinder 64 is actuated to move the rod 66 forward. The firstgripping member 30 is pressed by the presser plate 68. As a result, asshown in FIG. 8, the first gripping member 30 moves forward in thedirection indicated by the arrow D, causing the first protrusion 8 tofit into the recess 70. The hollow cylindrical body W2 is now gripped bythe first gripping member 30 and the second gripping member 32, andhence is prevented from being opened back into a plate shape.

Then, the cylinder 52 is actuated to retract the rod 54. At this time,the cylinder 52 is angularly moved about its portion which is pivotallysupported by the brackets 50, 50. The joint arm 58 is retracted to turnthe rotary board 46. The slanted pedestal 60 and the support member 28are turned about their portions which are coupled to the rotary board 46until finally the support member 28 abuts against the stopper 76 and ispositioned to extend from the first columnar member 24 to the secondcolumnar member 26, as shown in FIG. 9. At this time, the support member28 is inclined with respect to the horizontal direction (see FIG. 7).

Then, the cylinder 86 is actuated to elevate the rod 88. The first arm92 and the second arm 94 that are coupled to the bracket 89 by the rod90 are angularly lowered about their portions which are coupled to thefirst shaft engaging member 78 and the second shaft engaging member 80,respectively, by the joint rod 96. As a result, as shown in FIG. 10, theprismatic bar members 34 a, 34 b are brought into abutment against theouter circumferential wall surface of the hollow cylindrical body W2.Thus, the outer circumferential wall surface of the hollow cylindricalbody W2 is pressed by the prismatic bar members 34 a, 34 b, and theinner circumferential wall surface of the hollow cylindrical body W2 ispressed by the support member 28. Stated otherwise, the hollowcylindrical body W2 is clamped between the support member 28 and theprismatic bar members 34 a, 34 b and hence is reliably prevented frombecoming open back into a plate shape.

Then, the linear abutting regions of the hollow cylindrical body W2,i.e., the end faces 1, 2 thereof, are friction-stir-welded by thefriction stir welding tool 100.

Specifically, the friction stir welding tool 100 is inserted into thegap 98 (see FIG. 6) and the rotor 102 is rotated, after which the probe104 is held in sliding contact with the second protrusion 9 at anydesired position thereon. The sliding contact produces frictional heat,softening the region of the second protrusion 9 which is contacted bythe probe 104, whereupon the tip end of the probe 104 is plunged intothe first protrusion 8.

At a left end in FIG. 11 of the hollow cylindrical body W2, thedirection of a vector V1 along the rotational direction (indicated bythe arrow X) at a portion of the probe 104 that is most spaced from aboundary line L2 between the end faces 1, 2 is opposite to the direction(indicated by the arrow A) in which the probe 104 is displaced. In thedescription which follows, the end of the hollow cylindrical body W2where the direction of the vector V1 is opposite to the direction inwhich the probe 104 is displaced is referred to as “retreating side”.

At a right end in FIG. 11 of the hollow cylindrical body W2, thedirection of a vector V2 along the rotational direction (indicated bythe arrow X) at a portion of the probe 104 that is most spaced from theboundary line L2 between the end faces 1, 2 is the same as the direction(indicated by the arrow A) in which the probe 104 is displaced. In thedescription which follows, the end of the hollow cylindrical body W2where the direction of the vector V2 is the same as the direction inwhich the probe 104 is displaced is referred to as “advancing side”.

Usually, as shown in FIG. 12, the probe 104 is plunged such that thecentral axis L1 of the probe 104 is aligned with the boundary line L2.At this time, the size of a stirred region Z2, i.e., the amount ofmaterial that is stirred, is greater on the retreating side than on theadvancing side. Therefore, the material at the lower end along theboundary line L2 may not sufficiently be stirred, possibly with theresult that an unjoined region UN remains in the material. It isinferred that the unjoined region UN remains because the material tendsto cause a greater plastic flow on the retreating side than on theadvancing side. In FIG. 12, the reference characters Z1 represent aregion where the material is softened due to frictional heat.

Therefore, as shown in FIG. 13, it is preferable that the central axisL1 of the probe 104 be displaced from the boundary line L2 between theend faces 1, 2 of the first protrusion 8 toward the advancing side. Thatis, the probe 104 is plunged into the abutting regions at a positiondisplaced to the advancing side.

The distance D between the central axis L1 of the probe 104 and theboundary line L2 is set to a range equal to or smaller than the radiusof the probe 104. If the distance D is set to a distance in excess ofthe radius of the probe 104, then during the friction stir weldingprocess, more material is stirred on the advancing side, also resultingin an unjoined region UN that remains. The distance D should preferablybe equal to or smaller than one-half of the radius of the probe 104.

The probe 104 is plunged into the abutting regions at a positiondisplaced to the advancing side. The distance D (see FIG. 13) is set toa distance equal to or smaller than the radius of the probe 104,preferably equal to or smaller than one-half of the radius of the probe104. In this manner, the size of the stirred region Z2 is substantiallyequalized on the retreating side and the advancing side. Statedotherwise, the amount of stirred material is substantially equalized onthe retreating side and the advancing side.

By thus displacing the central axis L1 of the probe 104, which is in arange equal to or smaller than the radius of the probe 104, from theboundary line L1 between the end faces 1, 2 toward the advancing side,the amount of stirred material is substantially equalized on theretreating side and the advancing side. Since the stirred region Z2reaches to the lower end (back surface 4) along the boundary line L2, anunjoined region UN (see FIG. 12) is prevented from remaining. Therefore,a joint having excellent bonding strength is obtained.

As an unjoined region UN is prevented from remaining, a gap G (see FIG.13) is increased. The gap G may be managed so as to be equal to or lessthan 0.4 mm. Consequently, the managed value of the gap G is 0.3 mmgreater than the gap described above. According to the friction stirwelding process, even though the managed value of the gap G is only 0.3mm greater than the conventional gap, an operation for forming the gap Gis made highly easy to perform, and the time required to perform theoperation is greatly reduced.

Furthermore, because the crests of the sags 6 a, 6 b are held inabutment against each other on the outer circumferential wall surface(see FIG. 5), the gap formed between the end faces 1, 2 on the innercircumferential wall surface is reduced, and the area of contact betweenthe end faces 1, 2 is increased. Consequently, a large amount ofmaterial is stirred, producing a large amount of frictional heat. As aresult, a large number of large cavities are prevented from beingcreated in the joint.

While the rotor 102 is rotating, the friction stir welding tool 100 ismoved toward the first protrusion 8 (see FIG. 9). The material in thesoftened abutting regions of the hollow cylindrical body W2 isplasticized as it is stirred by the probe 104. After the probe 104 movesaway, the plasticized material is cooled and solidified into asolid-state joint. This phenomenon is successively repeated to join theabutting regions of the hollow cylindrical body W2 integrally into asolid-state joint.

When the probe 104 moves, since the hollow cylindrical body W2 isinclined with respect to the horizontal direction, the area of contactbetween the hollow cylindrical body W2 and the probe 104 is smaller thanif the hollow cylindrical body W2 is supported horizontally.Consequently, the probe 104 suffers a less load.

When the friction stir welding tool 100 moves, it is gradually loweredby a tilting mechanism, not shown, at a rate commensurate with thegradient of the hollow cylindrical body W2. Thus, the probe 104 isprevented from being released from the hollow cylindrical body W2.

As described above, the hollow cylindrical body W2 has the firstprotrusion 8 and the second protrusion 9, the first protrusion 8 and thesecond protrusion 9 are gripped by the first gripping member 30 and thesecond gripping member 32, and the hollow cylindrical body W2 is grippedby the support member 28 and the prismatic bar members 34 a, 34 b.Therefore, the hollow cylindrical body W2 is reliably prevented frombeing opened back into the plate-like workpiece W1, allowing thefriction stir welding process to be performed with ease.

According to the friction stir welding process, the butting regions canbe joined without forming swellings, and hence the welded hollowcylindrical body does not need to be finished. Consequently, it ispossible to manufacture a wheel rim of good appearance efficiently.

After the hollow cylindrical body W2, which serves as a preform for awheel rim, is fabricated by the friction stir welding process, thecylinder 86 is actuated to lower the rod 88, spacing the prismatic barmembers 34 a, 34 b away from the hollow cylindrical body W2. Thecylinder 52 is actuated to move the rod 54 forward, turning the supportmember 28, and the cylinder 64 is actuated to retract the rod 66,spacing the second gripping member 32 away from the second protrusion 9.The hollow cylindrical body W2 with the first protrusion 8 and thesecond protrusion 9 can now be removed from the friction stir weldingapparatus 20.

After the hollow cylindrical body W2 is released from the support member28, the first protrusion 8 and the second protrusion 9 are cut off,whereupon a wheel rim in the form of the hollow cylindrical body W2 isproduced.

A friction stir welding apparatus according to a second embodiment willbe described below.

FIG. 14 is a perspective view of the friction stir welding apparatusaccording to the second embodiment, and FIG. 15 is a is across-sectional view taken along line XV-XV of FIG. 14. As shown inFIGS. 14 and 15, the friction stir welding apparatus 120 comprises abase 122 having a slightly slanted bottom (see FIG. 15), a columnarmember 124 as a first support means, a first support natural lockcylinder 126 and a second support natural lock cylinder 128 as a secondsupport means, a support body 130 supported by the columnar member 124,the first support natural lock cylinder 126, and the second supportnatural lock cylinder 128, for holding various means, and a support core132 placed on and coupled to an upper end face of the support body 130.

Each of the first support natural lock cylinder 126 and the secondsupport natural lock cylinder 128 is a support having a means forsmoothly locking a plunger under hydraulic pressure.

As shown in FIG. 15, the columnar member 124 that is vertically mountedon the base 122 has a bottom board 134 and an upstanding column board136 that are combined into a substantially L-shaped assembly, theupstanding column board 136 being supported by a support board 38. Astopper 140 is coupled to the upstanding column board 136.

As shown in FIGS. 14 through 16, a rail 142 is laid on the base 122. Thefirst support natural lock cylinder 126 and the second support naturallock cylinder 128 are movable along the rail 142.

Specifically, the rail 142 engages in engaging grooves defined inengaging brackets 144 (see FIG. 14), and a positioning bracket 146 isfixedly mounted on the engaging brackets 144. A housing bracket 152,which is irremovably mounted on the head of a piston rod 150 of adisplacement cylinder 148, is fixedly positioned on one side face of thepositioning bracket 146. The first support natural lock cylinder 126 andthe second support natural lock cylinder 128 are fixedly coupled to thepositioning bracket 146. Therefore, when the piston rod 150 of thedisplacement cylinder 148 is moved forward and backward, the firstsupport natural lock cylinder 126 and the second support natural lockcylinder 128 are displaced while being guided by the rail 142.

The displacement cylinder 148 is supported by a substantially L-shapedsupport board 154 coupled to the base 122. A stop board 156 is mountedon the base 122 in a position confronting the displacement cylinder 148.When the positioning bracket 146 reaches a predetermined position, thepositioning bracket 146 and hence the first support natural lockcylinder 126 and the second support natural lock cylinder 128 areprevented from being further displaced by the stop board 156.

The first support natural lock cylinder 126 and the second supportnatural lock cylinder 128 have respective support rods 158, 160 that canbe lifted toward and lowered away from the support body 130.

As shown in FIG. 15, the support body 130 has a first insertion hole 162and a second insertion hole 164 that are defined longitudinally therein.The support body 130 also has a cam insertion slot 166 whichcommunicates with the first insertion hole 162 and is wider than thefirst insertion hole 162, the cam insertion slot 166 having a closedend. The bottom of the support body 130 is partly cut off, providing arecess 168 communicating with the cam insertion slot 166. The recess 168has a width greater than the cam insertion slot 166.

A horizontal pressing cylinder 170 serving as a first pressing means forhorizontally pressing the inner circumferential wall surface of thehollow cylindrical body W2 is fixedly coupled to an end of the supportbody 130. The horizontal pressing cylinder 170 has a piston rod 172 thatis inserted, together with a cam 174 shown in FIG. 17, in the firstinsertion hole 162. A bushing (not shown) is interposed between thepiston rod 172 and the support body 130.

As shown in FIG. 17, the head of the piston rod 172 is coupled to thecam 174 by a coupling annular member 176. As described later, as thepiston rod 172 moves forward and backward, the cam 174 causes small rods178 a through 178 c to move forward and backward in directionsperpendicular to the directions in which the piston rod 172 movesforward and backward.

The cam 174 has engaging grooves 180 a through 180 c defined in itsupper surface which are inclined at given angles with respect to thelongitudinal direction of the cam 174. The small rods 178 a through 178c have respective teeth 182 a through 182 c disposed on their bottomsurfaces and held in sliding engagement in the engaging grooves 180 athrough 180 c (see FIG. 15).

The cam 174 is held in the support body 130 by a holder 184 inserted inthe recess 168 and coupled to the support body 130.

As shown in FIG. 15, a flat-plate bracket 350 is fixedly coupled to theholder 184. A stay 352 extending vertically downwardly is fixed to theflat-plate bracket 350. A vertical pressing arm 358 (second pressingmeans) has a longer member 354 having a round head and a shorter member356 bent and extending horizontally from the longer member 354. Thevertical pressing arm 358 has its bent corner pivotally coupled to thestay 352. Therefore, the vertical pressing arm 358 is angularly movableabout its own bent corner pivotally coupled to the stay 352. The head ofthe longer member 354 of the vertical pressing arm 358 is held inabutment against the inner circumferential wall surface of the hollowcylindrical body W2.

An L-shaped stay 362 is mounted on the holder 184 at a positionconfronting a columnar projection 360 that extends horizontally from thebent corner of the vertical pressing arm 358. The columnar projection360 and the L-shaped stay 362 have respective through holes definedtherein, and a helical spring 364 has hooks engaging in these throughholes, respectively. The helical spring 364 normally biases the columnarprojection 360 vertically upwardly under its compressive forces. As thecolumnar projection 360 is pulled upwardly, the vertical pressing arm358 is resiliently urged to move toward the inner circumferential wallsurface of the hollow cylindrical body W2 about the bent corner of thevertical pressing arm 358. As a result, the head of the longer member354 of the vertical pressing arm 358 is pressed downwardly against theinner circumferential wall surface of the hollow cylindrical body W2.

The vertical pressing arm 358 is limited against its angular movement bya stopper screw 366 held against the shorter member 356. Therefore, thevertical pressing arm 358 is prevented from pressing the innercircumferential wall surface of the hollow cylindrical body W2 underexcessive forces.

Pressers 186 are fastened to the respective distal ends of the smallrods 178 a through 178 c by bolts, not shown (see FIG. 17). The pressers186 have respective tip ends curved complementarily in shape to theinner circumferential wall surface of the hollow cylindrical body W2.

The second insertion hole 164 extends longitudinally through the supportbody 130 (see FIG. 15). An aligning cylinder 188 fixedly coupled to aright end face, as seen in FIG. 15, of the support body 130 has a pistonrod 190 including a universal joint and inserted in the second insertionhole 164.

An elongate floating rod 129 has an end coupled to the head of thepiston rod 190. The other end of the floating rod 129 projects from thesecond insertion hole 164.

As shown in FIG. 18, the support body 130 has a first rod insertionsmall hole 194 and a second rod insertion small hole 196 that aredefined in an end of the support body 130 on opposite sides of thesecond insertion hole 164. A first large rod 198 and a second large rod200 are inserted respectively in the first rod insertion small hole 194and the second rod insertion small hole 196.

Bearings (not shown) are interposed between the support body 130 and thefirst and second large rods 198, 200. The bearings are sealed by a firstcam 202 and a second cap 204 that are fitted respectively in the firstrod insertion small hole 194 and the second rod insertion small hole196.

A joint member 206 is held against the end face of the head of thefloating rod 192. The joint member 206 has a first through hole 208, asecond through hole 210, and a third through hole 212 that are definedtherein. A bolt 214 extends through the central second through hole 210and is threaded into the head of the floating rod 192.

The first large rod 198 and the second large rod 200 extend respectivelythrough the first through hole 208 and the third through hole 212, sothat the floating rod 192 and the first and second large rods 198, 200are coupled to each other by the joint member 206. The first large rod198 and the second large rod 200 are prevented from being removed fromthe first through hole 208 and the third through hole 212 by annularstoppers 216. The floating rod 192 is prevented from being removed fromthe second through hole 210 by the end face of the head of the floatingrod 192 and a bolt 214.

A placement joint member 218, which has a vertical dimension shown inFIG. 15 slightly smaller than the joint member 206, extends between andis mounted on portions of the first large rod 198 and the second largerod 200 which extend from the first through hole 208 and the thirdthrough hole 212 in the joint member 206. Specifically, as shown in FIG.18, the placement joint member 218 has a fourth through hole 220 and afifth through hole 222 through which the first large rod 198 and thesecond large rod 200 extend, respectively. Bearings (not shown) areinterposed between the placement joint member 218 and the first largerod 198 and the second large rod 200. The bearings are sealed by a thirdcam 224 and a fourth cap 226 that are fitted respectively in the fourththrough hole 220 and the fifth through hole 222.

The first large rod 198 and the second large rod 200 extend further fromthe fourth through hole 220 and the fifth through hole 222,respectively, in the placement joint member 218. Casings 230 a, 230 bhousing respective helical springs 228 a, 228 b are mounted onrespective distal ends of the first large rod 198 and the second largerod 200.

The casings 230 a, 230 b have respective hollow cylindrical bodies 232a, 232 b fitted over respective circumferential side walls of the firstlarge rod 198 and the second large rod 200 and having respective openends, and respective hollow cylindrical covers 236 a, 236 b coupled tothe respective heads of the first large rod 198 and the second large rod200 by bolts 234 a, 234 b and having respective open ends. The hollowcylindrical covers 236 a, 236 b have respective circumferential sidewalls surrounding the respective circumferential side walls of thehollow cylindrical bodies 232 a, 232 b. The helical springs 228 a, 228 bhave ends seated on the bottom surfaces of the hollow cylindrical bodies232 a, 232 b and the top surfaces of the hollow cylindrical covers 236a, 236 b.

A first gripping member 238 is fixedly coupled to an upper end face ofthe joint member 206 (see FIG. 15). The first gripping member 238 has arecess 240 defined therein which is complementary in shape to the secondprotrusion 9. A substantially channel-shaped aligning presser member 242is mounted on an upper end face of the placement joint member 218 (seeFIGS. 15 and 19). The aligning presser member 242 is disposed insurrounding relation to the first gripping member 238 and has a distalend projecting beyond the distal end of the first gripping member 238.When the hollow cylindrical body W2 is set in place, the distal end ofthe aligning presser member 242 contacts the hollow cylindrical body W2earlier than the distal end of the first gripping member 238.

As described later, when the piston rod 190 (see FIG. 15) is moved, thefirst gripping member 238 and the aligning presser member 242 aredisplaced by the floating rod 192, the first large rod 198, and thesecond large rod 200.

As shown in FIG. 20, which is a cross-sectional view taken along lineXX-XX of FIG. 15, four tubes 244 a through 244 d for passing coolingwater therethrough are connected by pipe joints 245 to a right endportion of the support body 130 as seen in FIG. 15, i.e., an end portionof the support body 130 to which the aligning cylinder 188 and thehorizontal pressing cylinder 170 are fixedly connected. The support body130 has cooling water inlet passages 246 defined therein for introducingthe cooling water and cooling water outlet passages 248 defined thereinfor discharging the cooling water. The support body 130 also has an airpassage 250 defined therein that is connected to a compressed air tube(not shown) by a pipe joint.

The support core 132 which is fixedly positioned on the upper end faceof the support body 130 comprises a first core member 252 and a secondcore member 254. The inner circumferential wall surface of the hollowcylindrical body W2 abuts against a curved upper surface of the firstcore member 252, supporting the hollow cylindrical body W2 on thefriction stir welding apparatus 120.

The second core member 254 is placed on and coupled to an upper end faceof the support body 130. The second core member 254 has a slanted landdisposed on an upper end face thereof. The land has an insertion groove256 defined therein which extends in the longitudinal direction of thesupport body 130.

The second core member 254 has a first passage 258 and a second passage260 defined therein respectively on the opposite sides of the insertiongroove 256 (see FIG. 15). The first passage 258 and the second passage260 have upper passageways 262 extending from the right end to left endin FIG. 15 of the second core member 254, and lower passageways 264disposed below the upper passageways 262 and communicating with theupper passageways 262 in the left end in FIG. 15 of the second coremember 254. The lower passageways 264 extend from the left end to rightend in FIG. 15 of the second core member 254.

The upper passageways 262 of the first passage 258 and the secondpassage 260 communicate with the cooling water inlet passages 246, andthe lower passageways 264 of the first passage 258 and the secondpassage 260 communicate with the cooling water outlet passages 248.Therefore, the cooling water flows through the first passage 258 and thesecond passage 260.

Four upstanding pins 266 are mounted on the upper end face of the secondcore member 254 at confronting positions across the insertion groove 256near the right end portion in FIGS. 15 and 19 of the second core member254. The inner two of the pins 266 enter curved recesses 270 defined inthe second gripping member 268.

The first core member 252 is inserted and fixedly positioned in theinsertion groove 256 defined in the second core member 254. The firstcore member 252 has air ejection ports 274 defined therein near the pins266 and held in communication with the air passage 250 defined in thesecond core member 254.

The first core member 252 having the curved upper surface, and thesecond core member 254 having the first passage 258 and the secondpassage 260 for passing the cooling water therethrough are separate fromeach other. Therefore, the first core member 252 and the second coremember 254 can easily be fabricated.

The pressure of air ejected from the air ejection ports 274 is monitoredat all times by a first pressure sensor, not shown. The pressure ofcompressed air in the vicinity of the first finger 7 a and the thirdfinger 7 c of the hollow cylindrical body W2 is also monitored by asecond pressure sensor. The pressures of compressed air that aremonitored by the second pressure sensor and the first pressure sensorare compared with each other to judge whether the first finger 7 a andthe third finger 7 c are spaced from each other or held in abutmentagainst each other.

As shown in FIGS. 15 and 19, a gripping cylinder 278 is placed on theright end of the upper end face of the support body 130 with a fixedboard 276 interposed therebetween. The gripping cylinder 278 has apiston rod 280 and two guide members 281 a, 281 b (see FIG. 19). Apresser board 282 is mounted on the piston rod 280. The second grippingmember 268 is coupled to the presser board 282.

As described above, the curved recesses 270 are defined in the distalend of the second gripping member 268 in alignment with the pins 266.The second gripping member 268 also has a recess 284 defined thereinwhich is complementary in shape to the first protrusion 8.

A first aligning board 286 and a second aligning board 288 are fixedlypositioned on the right end of the upper end face of the support body130 in FIG. 19 at respective positions that confront each other acrossthe second core member 254.

The friction stir welding apparatus 120 also has, in addition to theabove means, a first presser stop means 290 a and a second presser stopmeans 290 b for pressing the hollow cylindrical body W2 to a stop. Thefirst presser stop means 290 a comprises a vertically movable cylinder294 fixedly mounted on an upper end face of a flat portion of thesupport board 292, an arm 302 coupled to a piston rod 296 of thevertically movable cylinder 294 and an upper end of a columnar portionof the support board 292 by respective links 298, 300, and a presserstop 304 mounted on the distal end of the arm 302. The presser stop 304has a longitudinal dimension that is essentially the same as thedimension of the hollow cylindrical body W2 in the longitudinaldirection B (see FIG. 14).

The second presser stop means 290 b is identical in structure to thefirst presser stop means 290 a. Those parts of the second presser stopmeans 290 b which are identical to those of the first presser stop means290 a are denoted by identical reference characters, and will not bedescribed in detail below.

When the presser stops 304 of the first and second presser stop means290 a, 290 b press the hollow cylindrical body W2 to a stop, a gap 306is created between the presser stops 304. The friction stir welding tool100 for welding the abutting end faces of the hollow cylindrical body W2is inserted in the gap 306.

As described above, the friction stir welding tool 100 has the rotor 102(see FIG. 14) fixed to a spindle, not shown, and the probe 104 mountedon the tip end of the rotor 102. The spindle is housed in a spindlecover 310.

A stay 312 is mounted on a side face of the spindle cover 310, and arotary actuator 314 is fixedly supported on the stay 312. The stay 312has a recess holding therein a box-shaped joint 316 having a passage(not shown) defined therein. To the joint 316, there are connected anair inlet tube 318 for delivering compressed cooling air that is to beejected toward the rotor 102, and a cooling air outlet tube 320.

The friction stir welding apparatus 120 according to the secondembodiment is basically constructed as described above. Operation andadvantages of the friction stir welding apparatus 120 will be describedbelow.

Prior to a friction stir welding process, the friction stir weldingapparatus 120 is supplied with a cooling water through the tubes 244 b,244 d.

The supplied cooling water is introduced through the cooling water inletpassages 246 defined in the support body 130 (see FIG. 15) into theupper passageways 262 of the first passage 258 and the second passage260 in the second core member 254. The cooling water flows from theright end to left end in FIG. 15 of the second core member 254, thenflows into the lower passageways 264, and flows through the lowerpassageways 264 from the left end to right end in FIG. 15 of the secondcore member 254.

The cooling water that has flowed through the lower passageways 264flows through the cooling water outlet passages 248 defined in thesupport body 130 (see FIG. 15), and is then discharged out of thefriction stir welding apparatus 120 through the tubes 244 a, 244 c.

The friction stir welding apparatus 120 is also supplied with compressedair via the non-illustrated compressed air tube. The compressed airpasses through the air passage 250 defined in the support body 130 andthe second core member 254, and is discharged from the air ejectionports 274 defined in the first core member 252.

After the cooling water and the compressed air have been introduced intothe second core member 254, the support core 132 (see FIGS. 14 and 15)is threaded through the hollow cylindrical body W2 having the firstprotrusion 8 and the second protrusion 9 (see FIG. 3), with the secondprotrusion 9 being positioned ahead. The hollow cylindrical body W2 isplaced on the support core 132, bringing the inner circumferential wallsurface of the hollow cylindrical body W2 into abutment against thecurved upper surface of the first core member 252 of the support core132.

The support core 132 has its longitudinal axis parallel to the directionin which the friction stir welding tool 100 is displaced. Therefore, thehollow cylindrical body W2 can be set in place along the direction inwhich the friction stir welding tool 100 is displaced. Since the hollowcylindrical body W2 does not need to be positioned in alignment with thedirection in which the friction stir welding tool 100 is displaced afterthe hollow cylindrical body W2 is set on the support core 132, thefriction stir welding process can quickly be performed.

The hollow cylindrical body W2 is displaced along the support core 132until a lower portion of one end face of hollow cylindrical body W2abuts against the stopper and an upper portion of the end face thereofabuts against the first aligning board 286 and the second aligning board288.

When the hollow cylindrical body W2 is displaced, the vertical pressingarm 358 is angularly moved about its bent corner as the helical spring364 is extended. Accordingly, the vertical pressing arm 358 does notpress the inner circumferential wall surface of the hollow cylindricalbody W2 to a stop. Stated otherwise, the vertical pressing arm 358 doesnot prevent the hollow cylindrical body W2 from being set in thefriction stir welding apparatus 120.

After the hollow cylindrical body W2 is displaced, the vertical pressingarm 358 is angularly moved about its bent corner as the helical spring364 is contracted. The vertical pressing arm 358 returns to its originalposition.

Then, the displacement cylinder 148 actuated to move the piston rod 150forward. The positioning bracket 146 is pressed thereby, displacing theengaging brackets 144 and hence the first support natural lock cylinder126 and second support natural lock cylinder 128 while being guided bythe rail 142.

When the engaging brackets 144 are displaced from the broken-lineposition to the solid-line position in FIG. 16, the positioning bracket146 abuts against the stop board 156. The first support natural lockcylinder 126 and second support natural lock cylinder 128 are preventedfrom being further displaced, and positioned in a given location belowthe support body 130.

Because the support rods 158, 160 of the first support natural lockcylinder 126 and second support natural lock cylinder 128 are positionedin the lower dead center when these cylinders are displaced, the supportrods 158, 160 do not abut against the support body 130. As the secondsupport means are provided by the first support natural lock cylinder126 and the second support natural lock cylinder 128, abutment of thesupport rods 158, 160 against the support body 130 is avoided.

Then, the first support natural lock cylinder 126 and the second supportnatural lock cylinder 128 are actuated to move the support rods 158, 160forward to the support body 130. Specifically, the support rods 158, 160are displaced upwardly in FIG. 16, supporting the support body 130 frombelow. The support body 130 and hence the hollow cylindrical body W2 aresupported at their opposite ends by the columnar member 124 and thefirst support natural lock cylinder 126 and the second support naturallock cylinder 128.

Then, the vertically movable cylinders 294 of the first presser stopmeans 290 a and the second presser stop means 290 b (see FIG. 14) areactuated to elevate the piston rods 296. The arms 302 are tilted towardthe hollow cylindrical body W2 about their portions joined to the links298, 300 until finally the presser stops 304 abut against the outercircumferential wall surface of the hollow cylindrical body W2 (seeFIGS. 15, 16, and 20)

Thereafter, the pressure applied to the piston rods 296 is reduced, andthe presser stops 304 are pressed under a reduced pressing force againstthe outer circumferential wall surface of the hollow cylindrical bodyW2. Finally, the resilient biasing force of the helical spring 364becomes greater than the pressing force of the presser stops 304.

The upper inner circumferential wall surface of the hollow cylindricalbody W2 is now placed on the support core 132, and the lower innercircumferential wall surface of the hollow cylindrical body W2 ispressed by the head of the longer member 354 of the vertical pressingarm 358. Since the resilient biasing force of the helical spring 364 isgreater than the pressing force of the presser stops 304 that are placedon the outer circumferential wall surface of the hollow cylindrical bodyW2, as described above, the hollow cylindrical body W2 is slightlystretched vertically downwardly. Therefore, the hollow cylindrical bodyW2 is prevented from deformed into a horizontally elongate ellipticalcross-sectional shape. As shown in FIG. 22, if the first finger 7 a andthe third finger 7 c or the second finger 7 b and the fourth finger 7 doverlap each other, these fingers are slightly corrected out of theoverlapping state as the hollow cylindrical body W2 is stretched asdescribed above.

Then, the horizontal pressing cylinder 170 (see FIG. 15) is actuated tomove the piston rod 172 forward. In response to the forward movement ofthe piston rod 172, the cam 174 (see FIG. 17) coupled to the head of thepiston rod 172 is moved forward.

When the cam 174 is moved forward, the engaging grooves 180 a through180 c in the upper surface of the cam 174 are displaced to press theteeth 182 a through 182 c that engage in the engaging grooves 180 athrough 180 c. The teeth 182 a through 182 c slide while being guided bythe engaging grooves 180 a through 180 c, causing the small rods 178 athrough 178 c to move forward and backward in the directionsperpendicular to the directions in which the cam 174 is moved forward,as indicated by the broken lines in FIG. 17. Finally, the pressers 186fastened to the respective distal ends of the small rods 178 a through178 c are pressed horizontally against the inner circumferential wallsurface of the hollow cylindrical body W2.

When the hollow cylindrical body W2 is thus pressed, the diameter of thehollow cylindrical body W2 is slightly increased. Stated otherwise, theabutting end faces of the hollow cylindrical body W2 are slightly spacedfrom each other. If the first finger 7 a and the third finger 7 c of thehollow cylindrical body W2 or the second finger 7 b and the fourthfinger 7 d of the hollow cylindrical body W2 overlap each other (seeFIG. 22), then they are brought out of the overlapping state as theabutting end faces are slightly spaced from each other. Since the hollowcylindrical body W2 is horizontally stretched, the hollow cylindricalbody W2 is prevented from being deformed into a vertically ellipticalcross-sectional shape.

After the overlapping state is eliminated, the piston rod 172 (see FIGS.15 and 17) is retracted to retract the pressers 186. The diameter of thehollow cylindrical body W2 is reduced, allowing the first finger 7 a andthe third finger 7 c or the second finger 7 b and the fourth finger 7 dto abut against each other without overlaps. The first protrusion 8 andthe second protrusion 9 are now formed.

According to the present embodiment, therefore, the innercircumferential wall surface of the hollow cylindrical body W2 isvertically and horizontally pressed. Because the hollow cylindrical bodyW2 is prevented from being deformed into a horizontally or verticallyelliptical cross-sectional shape, it is possible to obtain a highlytruly circular wheel rim.

Whether the end faces of the first finger 7 a and the third finger 7 care spaced from each other or not can be confirmed by compressed airejected from the air ejection ports 274 (see FIG. 19). If the end facesabut against each other with no gap defined therebetween, the compressedair is blocked by the first protrusion 8 and does not flow upwardly.Therefore, the pressure of compressed air that is monitored by thesecond pressure sensor in the vicinity of the first protrusion 8 ishigher than the pressure of compressed air that is monitored by thefirst pressure sensor in the vicinity of the air ejection ports 274.

However, if the end faces of the first finger 7 a and the third finger 7c are spaced from each other with a gap defined therebetween, thecompressed air passes through the gap and flows upwardly. Therefore, thepressure of compressed air that is monitored by the second pressuresensor is substantially the same as the pressure of compressed air thatis monitored by the first pressure sensor.

By comparing the pressures of compressed air that are monitored by thefirst pressure sensor and the second pressure sensor, it is possible toreliably detect whether the end faces of the first finger 7 a and thethird finger 7 c are spaced from each other or not. If the end faces ofthe first finger 7 a and the third finger 7 c are spaced from each otherwith a gap defined therebetween, then the piston rod 172 may further beretracted.

When the above process is finished, the tip ends of the first finger 7 aand the third finger 7 c and the tip ends of the second finger 7 b andthe fourth finger 7 d may be positionally displaced in the joiningdirection, as shown in FIG. 22. Moreover, the end face of the hollowcylindrical body W2 near the first protrusion 8 may be spaced from thefirst aligning board 286 and the second aligning board 288.

Then, the aligning cylinder 188 (see FIGS. 15 and 18) is actuated tocause the piston rod 190 to retract the floating rod 192 to the right inFIGS. 15 and 18. The first large rod 198 and the second large rod 200are now retracted, whereupon the joint member 206 and the placementjoint member 218 and hence the first gripping member 238 and thealigning presser member 242 (see FIG. 19) are displaced to the right inFIGS. 15 and 19.

As described above, the aligning presser member 242 has its distal endpositioned closer to the hollow cylindrical body W2 than the distal endof the first gripping member 238. Therefore, the distal end of thealigning presser member 242 initially abuts against the end face of thehollow cylindrical body W2.

The end face of the hollow cylindrical body W2 is displaced toward thefirst aligning board 286 and the second aligning board 288 by beingpressed by the aligning presser member 242. If the first finger 7 a isdisplaced prior to the third finger 7 c, then when the end face of aportion of the hollow cylindrical body W2 which has the first finger 7 aabuts against the first aligning board 286, the displacement of the endface of that portion of the hollow cylindrical body W2 is stopped. Asthe aligning presser member 242 is further displaced, the end face of aportion of the hollow cylindrical body W2 which has the third finger 7 cfinally abuts against the second aligning board 288. The displacement ofthe end face of the portion of the hollow cylindrical body W2 which hasthe third finger 7 c is stopped, and the end faces of these portions ofthe hollow cylindrical body W2 are aligned with each other. Statedotherwise, the end faces of these portions of the hollow cylindricalbody W2 lie flush with each other. When the end faces of these portionsof the hollow cylindrical body W2 are aligned with each other, thedisplacement of the aligning presser member 242 is also stopped.

The piston rod 190 and the floating rod 192 (see FIG. 18) arecontinuously retracted. At this time, inasmuch as the aligning pressermember 242 is pressed to a stop against the end face of the hollowcylindrical body W2, the placement joint member 218 and the aligningpresser member 242 are not displaced.

The first large rod 198 and the second large rod 200 cause the bolts 234a, 234 b and the hollow cylindrical covers 236 a, 236 b to compress thehelical springs 228 a, 228 b housed in the casings 230 a, 230 b. Thedistance by which the helical springs 228 a, 228 b are compressedproduces a further stroke by which the first large rod 198 and thesecond large rod 200 are displaced, allowing the joint member 206 andthe first gripping member 238 to be further displaced.

As a result of such displacement of the first gripping member 238, thesecond protrusion 9 is fitted into the recess 240. Since the process ofeliminating overlaps and the process of aligning the end faces have beenperformed as described above, the second finger 7 b and the fourthfinger 7 d of the second protrusion 9 fitted in the recess 240 do notoverlap each other, and the tip ends of the second finger 7 b and thefourth finger 7 d are not positionally displaced with respect to eachother.

Then, the gripping cylinder 278 is actuated to cause the piston rod 280to displace the presser board 282 and the second gripping member 268 tothe left in FIGS. 15 and 18. Finally, as shown in FIG. 19, the pins 266enter the respective curved recesses 270 defined in the second grippingmember 268, and the first protrusion 8 is fitted into the recess 284. Ofcourse, the first finger 7 a and the third finger 7 c of the firstprotrusion 8 do not overlap each other, and the tip ends of the firstfinger 7 a and the third finger 7 c are not positionally displaced withrespect to each other.

As the first protrusion 8 and the second protrusion 9 are fittedrespectively in the recesses 240, 284 of the second gripping member 268and the first gripping member 238, as described above, the hollowcylindrical body W2 is gripped by the first gripping member 238 and thesecond gripping member 268.

Then, a pressure is applied again to the piston rods 296 (see FIGS. 14and 16), causing the presser stops 304 to press the outercircumferential wall surface of the hollow cylindrical body W2. Thehollow cylindrical body W2 is now pressed from the side of its outercircumferential wall surface by the presser stops 304, and pressed fromthe side of its inner circumferential wall surface by the support core132. Stated otherwise, the hollow cylindrical body W2 is gripped by thesupport core 132 and the presser stops 304. Therefore, the hollowcylindrical body W2 is prevented from being opened back into a plateshape.

Then, the linear abutting regions of the hollow cylindrical body W2 arefriction-stir-welded by the friction stir welding tool 100.

Prior to the friction stir welding process, cooling compressed air isejected to the rotor 102. Specifically, the joint 316 is turned from theimaginary-line position in FIG. 14 by the rotary actuator 314 to bringthe curved tip end of the cooling air outlet tube 320 into confrontingrelation to the rotor 102. Then, compressed air is supplied from acompressed air source, not shown, and is ejected through the air inlettube 318, the joint 316, and the cooling air outlet tube 320 toward therotor 102.

Then, the friction stir welding tool 100 is inserted into the gap 306between the presser stops 304, and the rotor 102 is rotated, after whichthe probe 104 is brought into sliding contact with the first protrusion8 at any desired position thereon. When the probe 104 is brought intosliding contact with the first protrusion 8, frictional heat isproduced, softening the region of the first protrusion 8 that iscontacted by the probe 104, whereupon the tip end of the probe 104 isplunged into the first protrusion 8.

As with the friction stir welding process performed by the friction stirwelding apparatus according to the first embodiment, the central axis L1of the probe 104 is displaced from the boundary line L2 between the endfaces 1, 2 of the first protrusion 8 toward the end 2 a on the advancingside. That is, the probe 104 is plunged into the abutting regions at aposition displaced to the end 2 a on the advancing side.

Then, while the rotor 102 is rotating, the friction stir welding tool100 is moved toward the first protrusion 8. The material in the softenedabutting regions of the hollow cylindrical body W2 is plasticized as itis stirred by the probe 104. After the probe 104 moves away, theplasticized material is cooled and solidified into a solid-state joint.This phenomenon is successively repeated to join the abutting regions ofthe hollow cylindrical body W2 integrally into a solid-state joint.

Since the bottom of the base 122 is slightly slanted, the hollowcylindrical body W2 is also inclined with respect to the horizontaldirection. Therefore, when the friction stir welding tool 100 moves, thearea of contact between the hollow cylindrical body W2 and the probe 104is smaller than if the hollow cylindrical body W2 is supportedhorizontally. Consequently, the probe 104 suffers a less load.

When the friction stir welding tool 100 moves, it is gradually loweredby a tilting mechanism, not shown, at a rate commensurate with thegradient of the hollow cylindrical body W2. Thus, the probe 104 isprevented from being released from the hollow cylindrical body W2.

As described above, the hollow cylindrical body W2 has the firstprotrusion 8 and the second protrusion 9, the first protrusion 8 and thesecond protrusion 9 are gripped by the first gripping member 238 and thesecond gripping member 268, and the hollow cylindrical body W2 isgripped by the support core 132 and the presser stops 304. Therefore,the hollow cylindrical body W2 is reliably prevented from being openedback into a plate-like shape, allowing the friction stir welding processto be performed with ease.

The first finger 7 a and the third finger 7 c of the first protrusion 8do not overlap each other and are not positionally displaced from eachother. Of course, the second finger 7 b and the fourth finger 7 d of thesecond protrusion 9 do not overlap each other and are not positionallydisplaced from each other. Furthermore, since the hollow cylindricalbody W2 is highly truly circular, the end faces thereof remain inabutment against each other in the vertical direction as a whole withoutbeing positionally displaced. Therefore, the above friction stir weldingprocess makes it possible to manufacture a wheel rim having apredetermined diameter and length reliably and efficiently. That is, awheel rim having a very good dimensional accuracy can be obtained.

Friction stir welding is capable of welding abutting regions withoutproducing a swelling on the welded assembly and hence without the needfor finishing the welded assembly. Consequently, a wheel rim that isgood in appearance can be manufactured efficiently.

As the end faces suffer almost no vertical positional displacement,cavities are prevented from being produced in the joint.

While the friction stir welding process is being performed as describedabove, since the probe 104 is held in sliding contact with the hollowcylindrical body W2, frictional heat and machining heat are generated inthe hollow cylindrical body W2. The generated heat is transferred to thesupport core 132.

Since the cooling water flows in the second core member 254 of thesupport core 132, the heat transferred through the first core member 252to the second core member 254 is quickly removed by the cooling water.Consequently, the support core 132 is controlled not to exceed apredetermined temperature, e.g., 50° C. As the temperature of the hollowcylindrical body W2 is also prevented from rising, burrs are preventedfrom being formed on the hollow cylindrical body W2 in the middle of thefriction stir welding process.

The probe 104 for performing the friction stir welding process is alsocooled by the compressed air that is ejected from the cooling air outlettube 320. Therefore, the rotor 102 is prevented from being thermallyexpanded particularly toward the outer circumferential wall surface ofthe hollow cylindrical body W2. Because the probe 104 is plunged to asubstantially constant depth, it is possible to obtain burr-freeproducts of good dimensional accuracy successively.

After the hollow cylindrical body W2 is friction-stir-welded, thevertically movable cylinder 294 is actuated to lower the piston rod 296to space the presser stops 304 away from the hollow cylindrical body W2.The piston rod 280 of the gripping cylinder 278 is retracted to theright in FIG. 15, and the piston rod 190 of the aligning cylinder 188 ismoved forward to the left in FIG. 15. The first protrusion 8 is spacedfrom the second gripping member 268, and the second protrusion 9 isspaced from the first gripping member 238. The hollow cylindrical bodyW2 with the first protrusion 8 and the second protrusion 9 can now beremoved from the friction stir welding apparatus 120.

After the hollow cylindrical body W2 is released from the support core132, the first protrusion 8 and the second protrusion 9 are cut off,whereupon a wheel rim of highly good dimensional accuracy is obtained.

By thus preventing the first finger 7 a and the third finger 7 c fromoverlapping each other and also preventing the second finger 7 b and thefourth finger 7 d from overlapping each other with the horizontalpressing cylinder 170 and also by positioning the first finger 7 a andthe third finger 7 c and the second finger 7 b and the fourth finger 7 dwith the aligning cylinder 188, a wheel rim of highly good dimensionalaccuracy can be manufactured easily and efficiently.

While the first protrusion 8 and the second protrusion 9 are being cutoff, a next hollow cylindrical body W2 is set in the friction stirwelding apparatus 120. The next hollow cylindrical body W2 has its innercircumferential wall surface held in abutment against the curved uppersurface of the first core member 252 of the support core 132.

As described above, since the cooling water flows in the second coremember 254, the temperature of the second core member 254 is preventedfrom rising. Consequently, when a hollow cylindrical body W2 to befriction-sir-welded next is set in the friction stir welding apparatus120, heat is prevented from being transferred from the support core 132to the hollow cylindrical body W2 and hence the temperature of thehollow cylindrical body W2 is prevented from increasing. As the metallicstructure of the next hollow cylindrical body W2 is thus prevented fromchanging, the mechanical properties, such as mechanical strength, ofsuccessively manufactured wheel rims are prevented from varying.

Since the cooling water flows in the support core 132 that is held inabutment against the inner circumferential wall surface of the hollowcylindrical body W2, wheel rims of uniform quality can successively bemanufactured with utmost ease.

According to the present embodiment, a preform for a wheel rim has beendescribed as the hollow cylindrical body W2 by way of example. However,the present invention is not limited to such a preform.

The cooling medium is not limited to cooling water, but may be oil orthe like.

The friction stir welding process for friction-stir-welding a workpieceby displacing the probe 104 toward the advancing side is not limited tothe manufacture of the cylindrical body W2, but may be used tofriction-stir-weld end faces of different members.

The friction stir welding process for friction-stir-welding end faceshaving burrs and sags that are produced by shearing is not limited tothe manufacture of the cylindrical body W2. For friction-stir-weldingend faces of different members, sags of the end faces may be held inabutment against each other, and the probe 104 may be plunged from theend faces on the side where the abutting sags are present.

Although certain preferred embodiments of the present invention has beenshown and described by way of illustrative example, it is apparent thatin view of the disclosure, various changes and modifications may be madetherein by those skilled in the art without departing from the scope ofthe present invention.

1. A method of manufacturing a hollow cylindrical body, comprising thesteps of: bringing end faces of a plate material, having fingersprojecting from comers along a joining direction, into abutment againsteach other to form protrusions projecting along the joining directionwith end faces of the fingers, and also to form a hollow cylindricalbody; gripping said protrusions and friction-stir-welding abuttingregions of the end faces to join the end faces to each other, therebyforming a hollow cylindrical body having protrusions; and removing saidprotrusions.
 2. A method of manufacturing a hollow cylindrical bodyaccording to claim 1, wherein said hollow cylindrical body havingprotrusions is pressed from a side of an outer circumferential wallsurface thereof when the abutting regions are friction-stir-welded.
 3. Amethod of manufacturing a hollow cylindrical body according to claim 1,wherein the abutting regions are friction-stir-welded while said hollowcylindrical body is inclined with respect to the horizontal direction.4. A method of manufacturing a hollow cylindrical body according toclaim 1, wherein a wheel rim that is joined to a wheel disk to produce avehicular wheel is manufactured as said hollow cylindrical body.
 5. Afriction stir welding process for bringing a first end face and a secondend face of a metal workpiece into abutment against each other, andthereafter joining said first end face and said second end face to eachother with a rotating friction stir welding tool, wherein when a firstend having said first end face is present on a retreating side and asecond end having said second end face is present on an advancing side,a workpiece plunging member having a substantially circular crosssection, which is disposed on the tip end of said friction stir weldingtool, is plunged with a central region thereof being displaced from aboundary line between said first end face and said second end face tosaid second end within a range equal to or smaller than the a radius ofthe workpiece plunging member.
 6. A friction stir welding processaccording to claim 5, wherein said workpiece plunging member isdisplaced from said boundary line to said second end by a distance equalto or smaller than one-half of the radius of the workpiece plungingmember.
 7. A friction stir welding process according to claim 5, whereina workpiece having said first end face and a workpiece having saidsecond end face are separate from each other and are made of a chiefcomponent comprising the same metal.
 8. A friction stir welding processfor bringing a first end face and a second end face of a metal workpiecehaving a curved surface into abutment against each other to formabutting regions, and then friction-stir-welding the abutting regions tojoin said end faces to each other, wherein said first end face and saidsecond end face have burrs projecting in a thickness direction of saidmetal workpiece, and sags projecting in a direction transverse to saidthickness direction; when said abutting regions are formed, said sags ofsaid first end face and said second end face are disposed in confrontingrelation to each other and positioned on an outer circumferential wallsurface of said curved surface, and said burrs are positioned on aninner circumferential wall surface of said curved surface; and when theabutting regions are friction-stir-welded, a plunging member of afriction stir welding tool is plunged into the outer circumferentialwall surface on which said sags are disposed in confronting relation toeach other, and thereafter said friction stir welding tool is moved toscan said abutting regions.
 9. A friction stir welding process accordingto claim 8, wherein said first end face and said second end face arepresent on the same metal workpiece, and said abutting regions areprovided by curving said metal workpiece to bring said first end faceand said second end face into abutment against each other. 10-15.(canceled)
 16. A friction stir welding apparatus for bringing end facesof a plate material, having fingers at corners thereof, into abutmentagainst each other to form a hollow cylindrical body, andfriction-stir-welding said end faces to each other, comprising: a base;first support means and second support means which are mounted on saidbase; a support core spaced from said base by said first support meansand said second support means, for insertion into said hollowcylindrical body and for supporting said hollow cylindrical body; and afirst gripping member and a second gripping member disposed on saidsupport core for gripping respective protrusions, which are formed whenthe fingers are held in abutment against opposite ends of abuttingregions of said hollow cylindrical body, and which extend along ajoining direction; wherein said support core has passages definedtherein for passage of a cooling medium therethrough.
 17. A frictionstir welding apparatus according to claim 16, wherein said support corecomprises a first core member having a curved portion for abuttingagainst an inner circumferential wall surface of said hollow cylindricalbody and a second core member having a groove with said first coremember inserted therein.
 18. A friction stir welding apparatus accordingto claim 17, wherein said passages are defined in said second coremember.
 19. A friction stir welding apparatus according to claim 17,wherein said support core is spaced from said first support means andsaid second support means by being mounted on a support member.
 20. Afriction stir welding apparatus according to claim 17, further includingcooling means for cooling a rotating friction stir welding tool.
 21. Afriction stir welding apparatus for bringing end faces of a platematerial having fingers at corners thereof, into abutment against eachother to form a hollow cylindrical body, and friction-stir-welding saidend faces to each other, comprising: a base; first support means andsecond support means which are mounted on said base; a support membersupported by said first support means and said second support means;pressing means supported by said support member and movable forward orbackward by a displacing means, for pressing said hollow cylindricalbody from the side of an inner circumferential wall surface thereof; asupport core supported by said support member, for insertion into saidhollow cylindrical body and for supporting said hollow cylindrical body;and a first gripping member and a second gripping member disposed onsaid support core, for gripping respective protrusions, which are formedwhen the fingers are held in abutment against opposite ends of abuttingregions of said hollow cylindrical body, and which extend along ajoining direction.
 22. A friction stir welding apparatus according toclaim 21, wherein said pressing means comprises: a cam movable forwardor backward as said displacing means moves forward or backward; aplurality of rods engaging said cam and extending perpendicularly to thedirection in which said cam is movable forward or backward; and pressersmounted on respective distal ends of said rods, for pressing an innercircumferential wall surface of said hollow cylindrical body.
 23. Afriction stir welding apparatus according to claim 21, wherein saidsupport core has a discharge port defined therein for discharging acompressed gas.
 24. A friction stir welding apparatus for bringing endfaces of a plate material, having fingers at corners thereof, intoabutment against each other to form a hollow cylindrical body, andfriction-stir-welding said end faces to each other, comprising: a base;first support means and second support means which are mounted on saidbase; a support core spaced from said base by said first support meansand said second support means, for insertion into said hollowcylindrical body and for supporting said hollow cylindrical body; and afirst gripping member and a second gripping member disposed on saidsupport core for gripping respective protrusions, which are formed whenthe fingers are held in abutment against opposite ends of abuttingregions of said hollow cylindrical body, and which extend along ajoining direction; wherein either one of said first support means andsaid second support means is movable toward or away from said supportcore by a displacing means.
 25. A friction stir welding apparatusaccording to claim 24, further comprising a guide member for guidingsaid first support means or said second support means while said firstsupport means or said second support means is displaced.
 26. A frictionstir welding apparatus according to claim 24, wherein said first supportmeans or said second support means comprises natural lock cylinders,said natural lock cylinders having piston rods that are elevated tosupport said support core after the natural lock cylinders areinactivated.
 27. A friction stir welding apparatus for bringing endfaces of a plate material, having fingers at corners thereof, intoabutment against each other to form a hollow cylindrical body, andfriction-stir-welding said end faces to each other, comprising: a base;first support means and second support means which are mounted on saidbase; a support core spaced from said base by said first support meansand said second support means, for insertion into said hollowcylindrical body and for supporting said hollow cylindrical body; afirst gripping member and a second gripping member disposed on saidsupport core for gripping respective protrusions, which are formed whenthe fingers are held in abutment against opposite ends of abuttingregions of said hollow cylindrical body, and which extend along ajoining direction; two aligning boards held in abutment against an endface of said hollow cylindrical body and disposed one on each side ofabutting regions of said hollow cylindrical body; and aligning meanshaving a cylinder for pressing said hollow cylindrical body from theside of an opposite end face thereof, to displace the hollow cylindricalbody until said one face of the hollow cylindrical body abuts againstsaid aligning boards.
 28. A friction stir welding apparatus according toclaim 27, wherein either one of said first gripping member and saidsecond gripping member is displaced by said cylinder.
 29. A frictionstir welding apparatus according to claim 27, wherein said firstgripping member or said second gripping member is displaced and fitsover said protrusion of said hollow cylindrical body after displacementof the hollow cylindrical body has finished.
 30. A friction stir weldingapparatus for bringing end faces of a plate material, having fingers atcorners thereof, into abutment against each other to form a hollowcylindrical body, and friction-stir-welding said end faces to eachother, comprising: a base; first support means and second support meanswhich are mounted on said base; a support member supported by said firstsupport means and said second support means; a support core disposed onsaid support member, for insertion into said hollow cylindrical body andfor supporting said hollow cylindrical body; a first gripping member anda second gripping member disposed on said support core, for grippingrespective protrusions which are formed when the fingers are held inabutment against opposite ends of abutting regions of said hollowcylindrical body, and which extend along a joining direction; firstpressing means supported by said support member, for pressing an innercircumferential wall surface of said hollow cylindrical body verticallydownwardly with a resilient biasing means; and second pressing meanssupported by said support member and displaceable by displacing meansfor pressing an inner circumferential wall surface of said hollowcylindrical body horizontally.
 31. A friction stir welding apparatusaccording to claim 30, further comprising presser stop means forpressing said hollow cylindrical body from the side of an outercircumferential wall surface thereof to a stop.